Case hardening of glass sheets



Sept. 26, 1939. ,L. B AC 2,174,254

CASE HARDENING 0F GLASS SHEETS Filed March 13, 1937 r mmmuu v INVENTOR. 41. DVD MB. HQK

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Patented Sept. 26, 1939 2,174,254 case HARDENING or GLASS SHEETS Lloyd'V. Black, Tarentum, Pa., assignor to Pittsburgh Plate Glass Company, Allegheny County,

Pa., a corporation of Pennsylvania.

Application March 13, 1937, Serial No. 130,750

2 Claims.

The invention relates to the case hardening of glass sheets. In this operation, the sheet to be treated is ordinarily supported atone edge by tongs having hardened ends or points which tend to approach each other due to the weight of the sheet. The sheet, thus supported, is heated in a suitable furnace to a temperature at which the surface softens, after which it is removed from the furnace and subjected to cooling by air blasts.

It is a matter of some difiiculty to determine just when the glass has arrived at the proper temperature for removal from the furnace for the application of the chilling step, and it is the object of the present invention to provide a reliable means for guiding the operator at this stage of the operation. By the use of the improvement. the correct heating time is gauged, regardless of the furnace temperature, size of the sheet, or the composition of the glass, so that skill or experuniform product is secured. Briefly stated, this result is secured-by utilizing the movement of approach of the tong ends or points incident to the softening of the glass to complete an electrical circuit which actuates an indicating device, such as a hell or a lamp. A suitable apparatus is shown in the acompanying drawing, wherein:

Figure 1 is a side elevation, including a diagrammatic showing of the electrical connections The tongs are supported from the carriage frame (not shown) which moves the glass into and out of the furnace by means of the bar 8 and toggle arms 9, 9, so that the weight of the glass sheet tends to give the screws 1, I a movement of approach causing the screw ends to penetrate the glass when the glass softens.

Contact means are provided on the arms! and i in the form of the screw I ll mounted in the arm 3 and the block ll mounted in the arm 4, but insulated therefrom by a suitable bushing;

'A circuit is provided between the grounds I! and I3 on-the frame of the carriage which supports the bar 8, such circuit including the transformer coil 14, the wires l6, l6 and I1, and the winding ience is not required by the operator, and a more with the tong parts in the position occupied whenof the screws 1, 'l to permit of their adjustment.

of a bell l8. Current is supplied through the circuit due to the energizingof the transformer coil l9.

With the arrangement as described, the circuit is interrupted between the screw l0 and block I I as long as the glass is cold and the parts occupy the position of Fig. 1. When the glass becomes heated to the point at which its surface softens, the screws 1, 'l' penetrate the glass, as indicated in Fig. 2, so that the contacts l0 and l I approach and engage, thus completing the circuit through the winding of the bell l8, which sounds, thus warning the operator that it is time to remove the glass from the furnace and apply the chilling blasts of air to its surface.

In practice, I have found that the glass reaches the proper point for chilling when the screw points penetrate the glass about 4 so that the space between the contacts In and II is about the ratio to the short arms of the tongs to their long arms being 1 to 4. Since the contact screw I0 is adjustablathe degree of penetration of the screws 1,! into the glass before the electric circuit is completed, can be regulated to meet requirements.

. Any other suitable indicator may be used instead of the bell, such as a lamp or a metering device. Gripping devices other than the tongs might also be used, the only requirement being the application of means tending to penetrate the glass which move toward each other and complete a circuit due to such movement when the glass softens to a point permitting the desired degree of penetration. If desired, the tongs may be hung on the lower edge of the glass sheet with the bar 8 hanging downward and carrying a suitable weight to cause the tong ends to grip the sheet.

What I claim, is:

1. A device for use in case hardening a glass sheet, comprising tongs provided with a pair of opposing ends for gripping the edge of the sheet to be hardened and formed to penetrate the glass when it softens, means for supporting the tongs so that the weight of the glass sheet tends to cause a movement of approach of said ends toward each other, a pair of contact members carried by relatively moving parts of the tongs insulated from each other and adapted to engage when said ends are allowed, due to the softening of the glass, to approach each other a predetermined distance, an electrical circuit including said contacts, and an indicating device in the circuit.

2. A device for use in case hardening a glass sheet, comprising tongs provided with a pair of opposing ends for gripping the edge of the sheet to be hardened, and formed to penetrate the glass when it softens, means for applying the tongs in relation to the sheet so that force is applied tending to cause a movement of approach of said ends toward each other, a pair of contact members carried by relatively moving parts of the tongs insulated from each other and adapted to engage when said ends are allowed, due to the softening of the glass, to approach each other a predetermined distance, an electrical circuit including said contacts, and an indicating device 5 in the circuit.

LLOYD V. BLACK. 

